During vehicle start-up, it has been found desirable to run the motor initially at reduced power. This practice is referred to as a “soft-start.” One advantage of a soft start is to run the motor initially with reduced torque in the powertrain, which can allow the pinion to fully engage the ring gear prior to the motor being run at full power. In order to achieve a soft-start, present vehicle motors include a relay between the ignition switch and the solenoid that provides operating current to the motor. Examples of patent references that describe such configurations include U.S. Pat. Nos. 5,475,270, 5,892,422 and U.S. App. Pub. No. 2009/0002105.
A schematic of a prior art vehicle start system 100 that includes a relay 102 between the ignition switch 104 and the solenoid 106 is depicted in FIG. 1. The system 100 also includes a battery 108 and motor 110. In operation, when a vehicle operator turns the key, the ignition switch 104 allows power (about 1-5 amps, for example) to flow from battery 108 to relay 102. Relay 102 then allows power (about 250 amps, for example) to flow from battery 108 to solenoid 106. Energizing solenoid 106 allows power (about 250 amps, for example) to flow to motor 110 and begins solenoid plunger moving toward contacts 114 and 116. When solenoid plunger 112 abuts contacts 114 and 116, higher power (about 2000 amps, for example) flows from battery 108 to motor 110 via solenoid 106. The initial period when the motor is supplied lower power (about 250 amps, for example) provides a soft start.
However, the extra relay takes up space, is a potential point of failure and adds cost to the vehicle starting system.
Thus, there is a need for improved soft-start systems and methods for vehicles.